Warmer and drier than average temperatures continued for much of the nation in April.
These temperatures, when combined with the first quarter and previous 11 months, calculate to the warmest year-to-date and 12-month periods on record for the contiguous United States.
La Niña conditions in the equatorial Pacific transitioned to ENSO-neutral during Spring 2012. With ENSO-neutral conditions expected to continue through the June-August period, ENSO-related climate anomalies did not factor significantly into this outlook.
Over the previous several weeks, widespread soaking rains eased drought conditions in southwestern Texas and southeastern New Mexico, and a slow moving storm system brought relief to much of the Northeast and mid-Atlantic states.
Widespread rainfall across the upper Midwest also reduced existing drought conditions. In contrast, a combination of abnormal dryness and heat sparked rapid drought development across the middle and lower Mississippi Valley, while near-record heat across the Southeast was interrupted by hit and miss thunderstorm activity.
During the upcoming three month period, drought persistence is expected across the Great Basin and central Rockies due to a dry climatology, while the onset of the monsoon season may bring some relief to portions of the Southwest. Wet short and middle range forecasts and a rainy climatology increase prospects for improvement across the upper Midwest, while persistence is expected across the southern Plains and Mississippi Valley.
In the Southeast, sea-breeze convective activity will likely bring drought relief to Florida and coastal areas, but summer convection – outside of any tropical cyclone activity – is less likely to significantly reduce entrenched and exceptional drought conditions in the Piedmont.
Summer thunderstorms may bring some relief to the drought areas of the Northeast.
Sea surface temperatures in the eastern tropical Pacific Ocean swing back and forth every few years (sometimes more) like an irregular pendulum. The warm phase is known as El Niño; the cool phase—which it has been in for the past two winters—is called La Niña.
According to NOAA’s April 2012 ENSO Diagnostics Discussion, La Niña is fading and will likely be over by the end of April.
According to NOAA scientists, warmer-than-average temperatures dominated the northern and eastern regions of the U.S. this winter. Additionally, national snow cover extent was below average.
According to NOAA scienticts, record and near-record breaking temperatures dominated the eastern two-thirds of the nation and contributed to the warmest March on record for the contiguous United States, a record that dates back to 1895.
La Niña, which contributed to extreme weather around the globe during the first half of 2011, has re-emerged in the tropical Pacific Ocean and is forecast to gradually strengthen and continue into winter. Recently, forecasters with NOAA’s Climate Prediction Center upgraded last month’s La Niña Watch to a La Niña Advisory.
NOAA will issue its official winter outlook in mid-October, but La Niña winters often see drier than normal conditions across the southern tier of the United States and wetter than normal conditions in the Pacific Northwest and Ohio Valley.
The Southern Plains should prepare for continued drier and warmer than average weather, while the Pacific Northwest is likely to be colder and wetter than average from December through February, according to the annual Winter Outlook recently released by NOAA.
For the second winter in a row, La Niña will influence weather patterns across the country, but as usual, it’s not the only climate factor at play. The ‘wild card’ is the lesser-known and less predictable Arctic Oscillation that could produce dramatic short-term swings in temperatures this winter.
NOAA has issued its updated 2011 Atlantic hurricane season outlook, raising the number of expected named storms from its pre-season outlook issued in May
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